The invention relates generally to the field of lock and release mechanisms for telescoping or sliding paired members, more particularly relates to such mechanisms that allow the paired members to have three operational settings—a locked status precluding relative movement of the member pair, a closing status allowing relative movement of the paired members only in the direction toward each other to shorten the overall length of the combination of members, and a free travel status whereby the paired members can be moved in either direction relative to each. More particularly, the invention relates to such devices that utilize engaging opposing teeth of a ratchet bar type of construction. In particular, the invention is applicable for use with a sternal clamp device, and such an application shall be utilized to describe the invention herein.
A sternal clamp is a device that is used to secure two lateral halves of a sternum that has been longitudinally severed and divided in surgery, such as is often required to provide access to the interior of the chest cavity. The sternal clamp comprises a pair of sliding or telescoping clamp members, with each paired clamp member having means to grasp or abut the exterior edge of the sternum, such as single or multiple leg or hook members extending to the rear of the clamp member. The sternal clamp device is positioned across the sternum with the hook members positioned between adjacent ribs. The two clamp members are then compressed, i.e., moved toward each other in sliding fashion, to shorten the device and thereby pull the sternal halves together. The clamp members are then locked or secured in this contracted position by various mechanical means. Examples of sternal clamps can be seen in U.S. Pat. No. 4,201,215 to Crossett et al., U.S. Pat. No. 4,279,248 to Gabbay, U.S. Pat. No. 4,802,477 to Gabbay, U.S. Pat. No. 5,928,231 to Klein et al., U.S. Pat. No. 6,007,538 to Levin, U.S. Pat. No. 6,051,007 to Hogendijk et al., U.S. Pat. No. 6,217,580 to Levin, and U.S. Pat. No. 6,540,769 to Miller, III. Alternatively, the sternal clamp may be provided with apertures to receive mechanical fasteners, often referred to as bone screws, which are driven into the sternum prior to compression of the sternal halves.
A problem with the known devices is that the locking mechanisms utilized to maintain the sternal clamp in the compressed or contracted position are typically cumbersome, difficult to adjust and difficult to remove. Some mechanisms are not releasable at all once the clamp has been compressed. Some mechanisms do not allow the clamp members to be extended once the device has been compressed. Some mechanisms require the use of screws or similar fasteners that can be dropped or lost by the surgeon during the clamping step. All of these problems are exacerbated in emergency situations where immediate removal of the sternal clamp is required, such that in many cases destruction of the clamp by sawing or the like is the only suitable method for rapid access.
It is an object of this invention to provide a lock and release mechanism that enables the sternal clamp to have three functional statuses or settings—a first status where the device is locked to preclude relative movement of the clamp members in either direction, a second status where the device can be compressed or shortened by sliding the clamp members toward each other, but where release or extension of the device is precluded, and a third status where movement of the clamp members in either direction is allowed, to the point where the clamp may even be disassembled. It is a further object to provide such a device where the status of the sternal clamp may be easily and quickly changed from one status to either of the remaining statuses, and where any status may be chosen at any time. It is a further object to provide such a device where removal of the device from the patient can be quickly and easily accomplished at any time.